Hey thanks for reporting this. I noticed that just the other day when I installed Microthemer on a brand new site. If it only shows once, it’s nothing to worry about (although it shouldn’t be showing at all). Try saving your settings again. If the error persists please send me login details for your site via this secure contact form: https://themeover.com/support/contact/
If the error goes away, you shouldn’t see it again. I will release a fix so that it doesn’t happen on new installs today or tomorrow.